1. Field of the Invention
The present invention relates to a sewing machine, and especially relates to a sewing machine for industrial use such as sewing of thick and heavy cloth.
2. Description of Prior Art:
Recently as a sewing machine for industrial use, those that stop at a regular position have been used to enable unskilled workers to work with high quality and high efficiency.
The general configuration of a prior art sewing machine is illustrated with reference to FIG. 9.
In FIG. 9, a sewing machine 1 is driven by an electric motor 3 via a belt 2. When a control pedal 4 is pressed down forward, a pedal sensor 5 detects depth of the control pedal 4. A speed signal generator 7 generates speed signals corresponding to output data from the pedal sensor 5. A controller 6 controls the motor 3 to rotate in a speed corresponding to press-down degree of the pedal 4, based on the speed signal from the speed signal generator 7. When the pedal 4 is restored to the neutral position, the rotation speed of the motor 3 is decreased. After that, rotation of the motor 3 is retained in a slow rotation speed until a needle position detector 8 detects that the needle reaches a first position to be stopped. Furthermore, when the needle position detector 8 issues an output signal, the motor 3 is stopped of the rotation and driving of the sewing machine 1 is also stopped. The above-mentioned operations are generally called the regular position stopping of the sewing machine.
Furthermore, when the pedal 4 is heeled back, the motor 3 rotates in a constant speed and when it stops the needle is stopped at a second position by receiving a signal from the needle position detector 8. At the second position, the needle is drawn out upward from the cloth (needle-up position), thereby to enable the cloth being taken out and in the sewing machine 1.
The above-mentioned conventional sewing machine having the regular position stopping mode, however, is designed for a light load, and if it were used for a heavier load it would have a disadvantage of overload of the motor 3 and inherent locking of the needle at a first stitch when a heavy cloth is newly inserted in the sewing machine. Such a disadvantageous phenomenon is especially conspicuous in case of using a thick needle for sewing thick and heavy cloth. In the worst case, sewing can not be done and the motor 3 may burn-out when such a trouble is left as it is. Accordingly, it has been necessary to increase power of the motor or to give an impetus to the sewing machine at a first stitch by human hand for sewing heavy load such as thick and heavy cloth by the conventional sewing machine.